An image forming device, such as a color laser printer or an inkjet printer, receives input image data expressing color in a predetermined color space (e.g., RGB color space) from a personal computer (PC) or the like. The image forming device converts the input image data into output image data expressing color in a color space (e.g., a CMYK color space) other than the original color space. The image forming device forms an image based on the output image data.